The healing of broken bones, damaged ligaments, arthritic joints and the like is oftentimes promoted by mechanical immobilization; and heretofore, surgical casts molded from layers of gauze-wrapped plaster of Paris have been rather widely employed for this purpose. The drawbacks of plaster casts, however, are well recognized. Rigid plaster dressings are notoriously heavy, cumbersome and uncomfortable. In addition, they exhibit low cast strength and resist the free circulation of air to an encased body part, air circulation being necessary to preserve the health of bandaged skin tissue.
Attempts have been made in the past to overcome the excessive weight and comparative fragility of plaster casts by fabricating thermoplastic resinous material into strips which may be warmed and shaped to the limb or other body part. These strips, however, must be heated in an oven to above 125.degree. F. in order to make them pliable, and then wrapped quickly on the patient. The temperatures involved closely approximate and sometimes exceed human tolerance levels; and this approach has, as a consequence, achieved no great popularity.
Casts of polyurethane which is foamed and shaped in situ have also been proposed. The prior art formulations used for this purpose, however, have required the chemical reaction of two separate components in place on the patient, thus exposing both the patient and his physician to the toxicity of the isocyanate component and to the heat of the exothermic reaction. Despite the obvious strength and low weight advantages of foamed polyurethane, medical casts of this material have not proved of general acceptability heretofore.